1. Field of the Invention
This invention relates to gas-fired appliances such as water heaters, space heaters and fireplaces and, more particularly, to a device for controlling components commonly found in gas-fired appliances, namely, dampers and valves.
2. Disclosure of Related Art
In a conventional gas-fired appliance a gas pipe delivers a fuel gas, such as natural gas, from a fuel source to both a pilot burner and to a main burner that are disposed proximate, or within, a combustion chamber. The gas pipe includes a pair of valves disposed within the gas pipe. The first valve controls the flow of fuel gas from the fuel source to the pilot burner. The second valve controls the flow of fuel gas to the main burner.
Conventional gas-fired appliances also typically include an exhaust vent or flue to direct emissions resulting from combustion away from the combustion chamber of the appliance and into an area, such as the outdoors, where the emissions can dissipate. Exhaust vents, however, also allow heat to escape from the appliance thereby reducing the efficiency of the appliance. As a result, conventional gas-fired appliances typically include dampers disposed within the exhaust vent. The damper opens prior to ignition of the main burner in the appliance to allow emissions from combustion to be evacuated from the appliance. When the main burner is extinguished, the damper closes to trap the remaining heat.
Conventional gas-fired appliances also include a device for controlling one or more of the valves within the gas pipe and the damper in order to open and close the valves and the damper in response to predetermined conditions. Referring to FIG. 1, a typical control device 10 for a gas-fired appliance is illustrated. The control device 10 includes a motor assembly 12, a cam 14, a printed circuit board 16 upon which a control circuit is mounted, and a mounting plate 18 to support the components of device 10. The motor assembly 12 includes an output shaft 20 extending therefrom and is mounted to plate 18 by one or more fasteners 22 that extend through mounting flanges 24 on assembly 12 and into posts 26 extending from plate 18. Cam 14 is disposed about output shaft 20 and is coupled to shaft 20 for rotation therewith. One end 28 of cam 14 extends through an aperture (not shown) in plate 18 and is configured to receive a shaft 30 connected to a plate 32 of a damper 34. Circuit board 16 supports a control circuit used to control one or more valves and damper 34 of the gas-fired appliance. The control circuit includes a plurality of control switches 36, 38, 40 that are selectively actuated by rotation of cam 14. Board 16 is coupled to mounting plate 18 by one or more fasteners 42 that extend through a housing 44 for switches 36, 38, 40 and into corresponding apertures in either plate 18 or a mounting member affixed to plate 18.
The above-described control device has several disadvantages. First, cam 14 is positioned responsive to mounting plate 18 as opposed to switches 36, 38, 40. In particular, the position of cam 14 is dictated by the aperture in mounting plate 18. As a result, cam 14 may not be assembled in a proper positional relationship relative to switches 36, 38, 40 and the control circuit may not operate properly. This disadvantage is exacerbated by the tight tolerances found in plate 18 which typically comprises a metal stamping. The position of circuit board 16 can be adjusted to compensate for this deficiency, but repositioning board 16 increases assembly time and is subject to assembly errors. A second disadvantage of the above-described control device is that the device is relatively expensive. Finally, the above-described control device includes a relatively large number of parts and requires a relatively large amount of assembly time.
There is thus a need for a device for controlling a gas-fired appliance that will minimize or eliminate one or more of the above-mentioned deficiencies.
The present invention provides a device for controlling a gas-fired appliance such as a water heater, space heater, or fireplace.
A device in accordance with the present invention for controlling a gas-fired appliance includes a motor assembly having a shaft extending therefrom and a cam coupled to the shaft for rotation therewith. The cam is coupled to a damper plate of the gas-fired appliance and the plate is configured to rotate with the cam responsive to rotation of the motor shaft. The device further includes a printed circuit board having a control switch mounted thereon. The cam is configured to selectively actuate the control switch upon rotation of the cam. The inventive control device may also include a mounting plate to which the motor assembly and circuit board may be mounted. The mounting plate may be an injection-molded, plastic part. In accordance with the present invention the cam is supported on the printed circuit board as opposed to the mounting plate. In one embodiment of the invention, a pair of support members are disposed on either side of a housing for the control switch on the printed circuit board and are fastened to the switch housing. The cam is then received and positioned by the support members.
A device in accordance with the present invention represents a significant improvement as compared to conventional control devices for gas-fired appliances. In the inventive control device, the cam is positioned relative to the circuit board and the control switches disposed on the board as opposed to being positioned relative to the mounting plate. As a result, an accurate positional relationship between the cam and the control switches is ensured. Second, the inventive control device is less expensive than conventional control devices because it requires fewer parts, may be assembled more quickly, and uses an injection-molded plastic mounting plate as opposed to a stamped metal mounting plate.
These and other features and objects of this invention will become apparent to one skilled in the art from the following detailed description and the accompanying drawings illustrating features of this invention by way of example.